identical to another in result"
According to SQL standard queries like 
"select t1.a as col from t1, t2 order by a" should return an error if
both tables contain field a.


mysql-test/r/order_by.result:
  Updated test to conform SQL-standard.
mysql-test/t/order_by.test:
  Updated test to conform SQL-standard.
sql/item.cc:
  find_item_in_list() has now one more out parameter which is not used
  in item.cc functions.
sql/mysql_priv.h:
  find_item_in_list(): Added boolean out parameter "unaliased" which
  indicates that we have found field by its original name and not by
  its alias in item (select) list.
sql/sql_base.cc:
  find_item_in_list(): Added boolean out parameter "unaliased" which
  indicates that we have found field by its original name and not by
  its alias in item (select) list. This means that additional check is
  required to ensure there will be no ambiguity if we would search for this
  field in all tables.
sql/sql_select.cc:
  find_order_in_list(): If we have found field in select list by its
  original name and not by its alias then we should perform additional
  check to ensure that there will be no ambiguity if we will search for
  this field in all tables. Also small cleanup.